EUMeTrain: Nowcasting CAL Module - Basic Nowcasting

Fog/Stratus

"We have looked at a synoptic scale example like a frontal cloud system with rather long lasting features, at a convective situation with small to meso scale cloud cells and a high degree of time variability. I want you now to look at a weather situation which can show all these qualities: fog and stratus. It can be very small scale in mountain valleys with a short time scale but also very extended with a long duration at the same location over big plain areas where fog/stratus can stay same even over days. And again, we want to use only the basic satellite material, IR and Visible images."

30 Januar 06/07.30 UTC - IR image
This is the fog situation on 30 January 06 at 07.30 UTC presented in the IR image, the HRVIS image without correction according to sun elevation and finally the HRVIS image with correction according to sun elevant (LCC - Lambertsche Cosinus Correction).

In the HRVIS images the Danube valley in Austria and Bavaria, North and East Austria and big parts of Hungary show the typical cloud structure of fog. Especially the clear cut cloud edges at the mountain chains are typical, also the snow structure in the cloud free mountains. But besides the extended fog areas this example shows also valley fog in the Alps. Especially distinct is the fog in a NE - SW oriented valley in East Austria (Mürz - Mur rivers).

While it is very easy to recognise the bright fog area in the HRVIS images it is not easy to do the same in the IR image. While at the northern and the eastern boundary of the Alps the dark grey areas with the clear cut edges at the mountain chain can be diagnosed as fog/stratus is the area over Hungary even darker which would indicate no cloudiness. This diagnosis contradicts with the bright colours in the HRVIS image and so it has to be clarified if the diagnosis of fog in this area is correct.

 
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